The present invention refers to a bicycle front derailleur body, as well as to a device for adjusting its position on a bicycle frame.
In the context of this description and of the following claims, the bicycle derailleur of interest is the front one, which moves the chain between the different crowns associated with the crank arms. The movement of the chain is typically actuated through movement of a suitable thrusting member, commonly known as fork cage, associated with an operation kinematic mechanism.
In addition to the most common bicycle derailleurs, which are manually operated, there are also derailleurs with motorised operation in which the movement of the cage is carried out by a suitably controlled driving member, typically electrically controlled.
In any case, the front bicycle derailleurs comprise a derailleur body where the cage is mounted with the respective operation kinematic mechanism. The derailleur body is fixed to the bicycle frame, typically to the so-called seat tube of the frame (i.e. the one located under the saddle).
In the prior art the fixing of the derailleur body is carried out through coupling between a suitable support element projecting from the seat tube (typically welded on it) that forms a shaped seat for a corresponding coupling portion of the derailleur body. The coupling is completed by tightening a nut that locks the coupling portion to the support element.
At the end, the derailleur body is mounted substantially cantilevered on the projecting support element of the seat tube.
The Applicant has pointed out that the known coupling between derailleur body and seat tube has various drawbacks the main one being that, on the occasion of gearshifting, the positioning of the derailleur body with respect to the seat tube can undergo variations.
This occurs due to the fact that a reaction force acts on the derailleur body, the reaction force being substantially equal and opposite to the force applied by the cage on the bicycle chain, which determines a stress—on the coupling portion of the derailleur body and on the support element of the seat tube—such as to be able to induce a deformation of the coupling portion and of the support element. This deformation in turn causes a variation of the position of the derailleur body, which is pushed towards the seat tube. This movement of the derailleur body depends on the tension of the chain: the cyclist, especially a professional one, does not slow down pedalling on the occasion of gearshifting, for which reason the stress of the chain on the cage is high and the force that must be applied by the cage to move the chain is correspondingly high.
The result is that, since the derailleur body moves itself, the position of the relative cage acting on the chain also changes, which causes imprecision in gearshifting, which can even cause the chain to fall. This type of drawback is particularly serious in the case of derailleurs with motorised operation, in which the gearshifting precision is essential, since the cyclist cannot make any kind of correction or adjustment as he can do, on the other hand, by acting on the manual operation of a conventional non-motorised derailleur.
The technical problem at the basis of the present invention is to provide a bicycle front derailleur body that keeps a correct position in every condition of use and that therefore ensures a high precision and speed of gearshifting, so as to overcome the drawbacks mentioned above with reference to the prior art in a simple and effective manner.